What is a four-stroke engine and how does it work?

A four-stroke engine refers to the number of strokes a piston makes in one cycle, or in two rotations of the crankshaft. The four strokes are intake, compression, power, and exhaust. During the intake stroke, the piston travels down the cylinder to let fresh air/fuel in through the intake valve (Mechanical Booster). The air/fuel mixture is sucked into the cylinder because "the piston is an airtight seal inside the cylinder... " which "...creates a partial vacuum" (EpicPhysics.com). The compression stroke starts as the piston travels up the cylinder and compresses the fuel/air mixture (Jenkins). Then a "spark plug ignites the..." fuel/air mixture, forcing the piston down the cylinder during the power stroke (Jenkins). It is important to note that the power stroke "... is the only point at which the engine creates energy" (EpicPhysics.com). Moreover, "as the piston moves up and down in the cylinder it rotates the crankshaft" (AutoEducation). Lastly, once the piston completes the power stroke, "the exhaust valve opens" to expel the exhaust gasses (AutoEducation).


When compared with a two-stroke engine, the four-stroke engine has a few advantages. For instance, four-stroke engines “have a dedicated intake, power and exhaust stroke, which keeps fuel-to-exhaust crossover to a minimum” (Rowe). This is referring to the loss of fresh fuel/air mixture when the intake port and the exhaust port are open at the same time during the two-stroke engines cycle. This means that the four-stroke engine is more fuel efficient (mBuyNowBlog). Also, generally speaking, a 4-stroke engine will last longer than a two-stroke engine “because 2-strokes must rev to very high RPM to make any power…”(Rowe). Additionally, in comparison with a two-stroke engine, the four-stroke engine has more torque (mBuyNow Blog) because of the "the efficiency of the fuel burn" (Rowe.)

Lastly, two-strokes “tend to run very dirty” because oil has to be mixed with the fuel “to lubricate the crankcase” which is in contrast to the four-stroke engines with their “dedicated oiling system that’s largely separate from the combustion chamber…” (Rowe). More specifically, four-stroke engines are cleaner because two-stroke engines burn the oil that has to be added to the two-stroke engine's fuel (mBuyNow Blog).


Despite the conveniences of the four-stroke engine, there are a few drawbacks such as "more parts to worry about... which..." makes it harder to diagnose issues and makes four-stroke engines "more expensive and complex" (mBuyNow Blog). Moreover, it should be noted that four-stroke engines are not as powerful as two-stroke engines when you consider that “the four stroke [engines] fire once every two revolutions, while the two stroke engines..." have a power stroke in every revolution (mBuyNow Blog). Also, in comparison to the four-stroke engine, "two-stroke engines can work in any orientation [...] A standard four-stroke engine may have problems with oil flow unless it is upright" illustrating the four-stroke engine's limitations in certain applications (Brain). However, despite these challenges, the four-stroke engine is everywhere.

We want to know: what do you like better, a two-stroke engine or a four-stroke engine?


“4 Stroke Engine Advantages and Disadvantages.” mBuyNow Blog. n.p., 3 June, 2013. Web. 26 August, 2015.

Brain, Marshall. "How Two-stroke Engines Work." HowStuffWorks. InfoSpace LLC, 1 April, 2000. Web. 27 August, 2015.

"How does a Four Stroke Petrol Engine Works?" Mechanical Booster. Mechanical Booster, n.d. Web. 25 August, 2015.

"How a Four Stroke Engine Works 1." EpicPhysics.com. EpicPhysics.com, n.d. Web. 25 August, 2015.

Jenkins, Richard. "How cars work - The Workings of a Car Explained." Driving-Test-Success.com. Richard Jenkins, n.d. Web. 26 August, 2015.

Rowe, Richard. “The Advantages of 4 Stroke Engines.” eHow. Demand Media, Inc., n.d. Web. 26 August, 2015.

"The Automotive Engine: How your car engine works..." AutoEducation. AutoEducation.com, n.d. Web. 26 August, 2015.

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